COURTESY ILLUSTRATION / UH INSTITUTE FOR ASTRONOMY
This painting by artist Karen Teramura shows how the four-star system studied by University of Hawaii astronomer Evgenya Shkolnik may have looked when it was first formed, possibly billions of years ago.

Isle scopes help find 4-star system

Two telescopes on the summit of Mauna Kea have contributed to the discovery of four nearby stars rotating around each other in a tight pattern like a dumbbell.

University of Hawaii astronomer Evgenya Shkolnik discovered the odd grouping 166 light-years away in 2006 using the giant Keck I telescope. She did two follow-up studies using the mid-sized Canada-France-Hawaii Telescope.

Until 2006, astronomers thought BD -22°5866 was a single star, Shkolnik said. But she noticed that the light from the object was rapidly shifting back and forth from reddish to bluish.

Shkolnik realized that meant two stars were spinning around each other. Eventually she realized that there were two more stars, balancing the other two at the end of a gravitational dumbbell the size of the orbit of Jupiter. All four stars are about half the mass of the sun.

The first two stars take just five days to spin around each other. The other two take 55 days.

The whole dumbbell spins around and returns to its original position in nine years. Jupiter, in a similar orbit around the sun, needs nearly 12 years to complete an orbit.

How long this cosmic spin has been under way is not clear, but it could be several billion years, Shkolnik said.

While groupings of stars moving around each other are fairly common, only 1 in 2,000 consists of so many stars in such a relatively small space, she said.

Shkolnik's work was presented at a recent meeting of the American Astronomical Society in Austin, Texas.